Stratospheric Ozone Depletion

Where is the ozone layer?

The ozone (O3) layer is located in the layer above the Earth´s troposphere known as the stratosphere. In the stratosphere ranging from 15-30 km (9-19 miles) is where O3 is concentrated, although the highest concentrations occur at 25 km (16 miles) of altitude. In the stratosphere, there is a temperature inversion caused when ultraviolet radiation is absorbed by O3 gas. The causes the layer to vary in thickness, being thinner in the equator and getting gradually thicker towards the poles. It also varies seasonally, being thicker in spring and thinner in autumn.

Depletion of Ozone

Depletion of O3 involves two different, although, related kinds of atmospheric processes that have occurred since the late 1970s. The first process, which has occurred for almost 40 years, is a decline per decade of an approximate amount of 4% of O3, and the second refers to great amounts of O3 decrease during springtime in the Earth´s poles.

The cause of depletion of ozone is mainly produced by atomic halogens, which stem from halocarbons refrigerants, including chlorofluorocarbons (CFCs), freons, halons, etc. The damage to this important layer in the stratosphere has been observed to increase as the emissions of halo carbons are increased.

Ozone-depleting substances is the name given to CFCs and other chemical substances that affect the concentrations of ozone gas. Ozone protects the Earth´s surface form the harmful UVB radiation. UVB radiation is known to affect humans with disorders, such as skin cancer, eye cataracts, immune system disorders, among others. Plants and animals are also affected by ozone depletion. A reduction on marine phytoplankton has been observed due to the phenomenon.

Ozone Hole

Credit: Public Domain via Wikimedia Commons

The Ozone Hole

The layer of ozone over the Antarctic continent has one of the greatest concentrations of this protective gas. Most of the O3 in Antarctica is produced in the tropics and carried to the Antarctic by blowing winds at high altitudes. During spring in the Southern hemisphere, which occurs in September and October, a belt of stratospheric winds, known as the polar vortex, encircles the Antartic region, isolating the Antarctic cold air from the mid-latitudes warm air.

during the long dark Arctic winter, temperatures within the polar vortex can descend down to -85 ºC (-121 ºF), allowing the formation of high altitude clouds. These clouds allow the chemical interactions of nitrogen, hydrogen and chlorine atoms, damaging the ozone layer.

Concerns about ozone depletion have led the international community to adopt measures, such as the Montreal Protocol, which bans the production of CFCs and other depleting substances.